A substrate for manufacturing an electronic component may be required to have through holes, through trenches, recessed portions, and the like formed therein. Whereas, an electric connection may be established, or an electric circuit may be formed by filling a conductive material in the through holes, the through trenches, and the recessed portions formed in the substrate, or forming a plated layer on the surfaces of the through holes, the through trenches, and the recessed portions.
For example, in a double-sided printed wiring board or a multilayer printed wiring board, connection of wiring patterns of the opposite sides or respective layers is carried out by silver through holes obtained by filling silver in the through holes formed in the substrate, or plated through holes obtained by plating the through holes. Further, as a semiconductor package, there is known an insertion type package to be mounted by inserting a lead introduced from the package to the substrate having through holes referred to as through holes.
As the hole processing methods for forming through holes in a printed wiring board, for example, mechanical processing methods such as blanking by a punching die and cutting processing by a drill are known. However, with such mechanical processing methods, fine processing may be difficult, or the methods are difficult to apply according to the material of the substrate.
Also in processing of trenches of a substrate for an electronic component, conventionally, the trenches have been formed by blanking with a die. However, the formation of flash upon blanking has been unfavorably inevitable. Under such circumstances, there has been proposed a method for subjecting a substrate for an electronic component having a metal foil on the surface to trench processing by water jet. More specifically, there is proposed a method in which the substrate is supported on a support provided with a water jet release hole to carry out trench processing by water jet, and thereby floating of the metal foil is prevented (see, e.g., Patent Document 1). However, with this method, the dimensions allowing trench processing depend upon the diameter of the jet of water jet. Therefore, fine processing is difficult, and in addition, the method is not suitable for processing trenches having a wide variety of patterns.
Conventionally, there has been proposed a method in which a glass thin plate or a sintered ceramic thin plate is sand blast processed to form through holes and recessed portions (see, e.g., Patent Document 2). Specifically, a resist pattern is formed on a glass thin plate or a sintered ceramic thin plate by a photo process. Thus, sand blast processing is carried out from above the resist pattern, thereby to process the positions and the shapes of the through holes and the recessed portions with high precision. In the resist pattern, an opening pattern corresponding to the through holes and the recessed portions is formed. Thus, the resist pattern serves as a mask during a sand blast processing. A conductive material is filled in the through holes and the recessed portions to form a wiring layer. A plurality of the wiring layers are stacked one on another to manufacture a multilayer wiring substrate.
Alternatively, the following method has been proposed. In a printed wiring board, openings each for passing there through a bonding wire to connect an electronic component to be mounted and a contact terminal are formed. At this step, the substrate covered with a resist for blast is subjected to sand blast processing, thereby to form the openings (see, e.g., Patent Document 3). As the substrate, a double-sided metal-laminated resin-coated substrate containing a glass fiber is used. In the resist for blast, an opening pattern corresponding to the openings is formed.
However, with a conventional sand blast processing, the formation of fine-pitch wiring, deep through holes, and deep trenches is difficult. The first reason for this is that the substrate to be subjected to a sand blast processing is a high hardness material such as a glass thin plate, a sintered ceramic thin plate, a resin substrate containing a glass fiber, or a resin laminated plate having a metal layer. The second reason is as follows: a mask material such as a resist for blast is required to be reduced in thickness as the pitch becomes finer; this however causes the mask itself to be incapable of standing a harsh sand blast processing or a long-time sand blast processing. Even in the case where a hard material such as a stainless steel thin plate is used as a mask material, when the object to be processed is a hard substrate, the mask pattern of fine through holes, through trenches, and the like, formed in the mask are chipped in the sand blast processing. Therefore, it is difficult to form deep through holes and trenches in the substrate with precision.    (Patent Document 1) JP-A-2000-246696    (Patent Document 2) JP-A-10-284836    (Patent Document 3) JP-A-11-102992
An object of the invention is to provide a method for manufacturing a porous material in which very complicated and fine through portions and recessed portions have been patterned, using a soft porous material in place of a conventional hard substrate material.
Particularly, another object of the invention is to provide a method for manufacturing a porous molded product or a nonwoven fabric in which fine through holes, trenches, and the like have been patterned with a processing method using a fluid such as a sand blast processing with a porous molded product or a nonwoven fabric targeted for processing under conditions causing less damages to a mask.
A still other object of the invention is to provide an electric circuit component made of a patterned porous molded product or nonwoven fabric in which a plated layer has been selectively formed on the surfaces of the through portions and the recessed portions.
The inventors conducted a close study in order to achieve the foregoing objects. As a result, they found the following fact. By a processing method in which a fluid is sprayed via a mask having through portions in a pattern, with a soft porous material, which has been conventionally considered very difficult or impossible to finely pattern by mechanical processing, targeted for processing, it is possible to obtain a porous material having through portions and recessed portions to which a pattern of fine through portions of the mask has been transferred. As the fluid, a fluid containing abrasive grains is preferably used.
The following fact was found. With this method, it is possible to carry out fine processing such as the formation of deep through holes and deep trenches without breaking the porous structure of the porous molded product. Further, a conductive metal is deposited on the surfaces of the through portions such as through holes and through trenches, and the recessed portions such as trenches formed by this method. As a result, it is possible to obtain a soft and elastic circuit substrate and an electric circuit component such as a member for the electric reliability inspection. This invention was completed based on these findings.